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The "Molecules and Materials" team was created in 1981 by Patrick Cassoux, then led by Lydie Valade (2003-2011). The team was at the source of the preparation of single crystals of many conductors and superconductors derived from coordination complexes but also molecular assemblies combining two physical properties : conductivity, magnetism, conductivity-spin transition, conductivity, photochromism.

Its recent activities include the preparation, the study of physico-chemical properties and the applications of nano-objects of molecular conductors and conductive polymers. We are currently focusing our efforts on systems well-known as single crystals or thin films to highlight any changes in physical characteristics caused by their size reduction.

Nanowires of molecular conductors

We have developed several techniques for preparing nanowires of molecular conductors on nano-structured or functionalized substrates. The CVD technique yielded nanowires of TTF∙TCNQ on austenitic steel or silicon conversion coating [1].
The dip coating and electrodeposition methods on Si substrate (001) led to nanowires of TTF[Ni(dmit)2]2 and (perylène)2[Au(mnt)2] [1-5] or nanorods of (TMTSF)2ClO4 [6]. TTF[Ni(dmit)2]2 nanowires ( 30 nm diameter) exhibit a transition to a superconducting state at 0.8 K under 7 kbar hydrostatic pressure [7].Nanowires of TTF∙TCNQ austenistic steel conversion coating (left) and nanowires of (perylène)2[Au(mnt)2] on nanoporous Si(001) (right)

Nanoparticles of molecular conductors

The synthesis of spherical nanoparticles of molecular conductors is a challenge because of the natural tendency of these compounds to grow as needles for which the growth axis coincides with the stacking of molecules (usually via π - π stacking). We were the first team, at the international level, to obtain (chemically or electrochemically) nanoparticles of molecular conductors built on TTF or BEDT-TTF units. The synthetic strategy is the addition of a "growth regulator" to the medium in which the reaction takes place. The "growth regulator" may be an ionic liquid (imidazolium salt or quaternary ammonium salt), amine or a long chain carboxylic acid or a polymer.

- Nanoparticles of TTF∙TCNQ were stabilized in organic medium (THF) by octylamine or octanoic acid (mean diameter ranging from 10 to 35 nm). They have a remarkable stability against aggregation and are being tested in electronic devices on satellites (coll. O. Vendier Thales-Alenia-Space et F. Courtade CNES) [14].AFM image of nanoparticles of TTF∙TCNQ stabilized by octylamine (mean diameter : 35 nm)

Nanoparticles of conducting polymers

Coordination polymers of [M(C2S4)]nNax type are known since 1975, and show conductivities up to 50 S/cm depending on the nture of the metal M and/or the cation (Na+ or else).Nanoparticles of [(NiC2S4)(BMIM)xNay]n.e(BMIM)(BF4)

Their development and their applications were not successful because of their total insolubility, whatever the solvent. Using the methods described above, we managed to get these polymers in a soluble form, thanks to their nanoparticle stabilized by ionic liquids such as (BMIM)(BF4).
Their composition as nanoparticles is [(NiC2S4)(BMIM)xNay]n.e(BMIM)(BF4). Due to the stabilizing layer around the nanoparticles, the electrical conductivities are lower than those of bulk polymers, and are of the order of 10-5 à 10-7 S/cm.